Gas turbines, such as aircraft engines for example, comprise at least one compressor and at least one turbine in addition to a combustion chamber. In gas turbines that comprise only a single compressor as well as a single turbine, the compressor and the turbine are connected with one another by a single rotating shaft. If the gas turbine has two compressors as well as two turbines, namely a low pressure compressor, a high pressure compressor, a high pressure turbine as well as a low pressure turbine, then the low pressure compressor as well as the low pressure turbine are connected with one another by a first shaft, and the high pressure compressor as well as the high pressure turbine are connected with one another by a second shaft. The two shafts then generally extend coaxially relative to one another, whereby one of the two shafts surrounds the other.
Overspeeding rotation conditions of a gas turbine as a result of a shaft break must be surely avoided. If a shaft break arises, then a compressor coupled with the broken shaft will no longer take-up any power from the corresponding turbine, whereby an overspeeding rotation of the turbine is caused. Because considerable damages can be caused on the gas turbine by the overspeeding rotation conditions, shaft breaks must be surely detected or identified, in order to shut off the gas turbine as a reaction thereto.
The DE 195 24 992 C1 discloses a method for regulating a shaft engine with a micro-control device with monitoring of the engine for shaft break and overspeeding rotation. According to the method disclosed therein, rotational speeds are measured with the aid of sensors, and the engine is tested with respect to shaft breakage and overspeeding rotation on the basis of these rotational speeds. If such an erroneous function is recognized, then the fuel delivery to the combustion chamber is interrupted and the gas turbine is deactivated.
In connection with the method disclosed in DE 195 24 992 C1, the determination of a difference rotational speed between a compressor-side end or section and a turbine-side end or section of the gas turbine shaft is necessary. Accordingly, rotational speeds must be detected at least two points, at a first compressor-side point and at a second turbine-side point. Especially in the hot turbine area, a rotational speed determination requires complicated provisions, whereby carrying out the method known from the prior art has been shown to be expensive and complicated. Furthermore, the method known from DE 195 24 992 C1 is only applicable on one or two-shafted gas turbines. On the other hand, this method known from the prior art is not practicable for multi-shafted gas turbines. This especially applies to more than two-shafted gas turbines, because a shaft surrounded by rotating shafts cannot easily without further efforts be referenced to a stationary reference system.